My house was built about 26 years ago. The first year the front yard sunk twice. We had the builder come out and fill it in each time. The builder also put in an ash tree. About 20 years ago all the ash trees in the neighborhood got infested with bag worms. We all had the trees removed along with the stump. Now the tree roots are decomposing and very large hard mushrooms are growing and I have been digging them up leaving large holes in my yard. What should I do to stop the mushrooms? Do I just fill in the holes with topsoil and seed? Should I have the yard tilled up because it is so compacted that the drainage is poor? Any advice would be appreciated. Thanks

Depends on the depth of the holes. Your really only need two to four inches of topsoil. But if you have to buy a load of topsoil anyhow and it is standard soil (not organic or mix containing waste products- in other words -good, easily compacted soil), filling completely with topsoil is OK.
Have you considered having a contractor grind the stumps completely out?